Persistent Photoconductivity in Strontium Titanate and Related Oxides

Washington State University, Pullman WA

Investigators

Abstract

Nontechnical description: The project investigates a unique property of persistent photoconductivity, recently observed at room temperature. Samples with this property experience a dramatic increase in electrical conductivity when exposed to light, which persists long after the light is turned off. Normally, this effect is observed at low temperatures, requiring coolants such as liquid nitrogen. Strontium titanate, a transparent crystal, exhibits large persistent photoconductivity at room temperature, opening up new possibilities for practical devices. The research team is attempting to identify and characterize the defect responsible for this novel behavior. The aim is to use this effect in an optical pen to define reconfigurable electronic circuits. The students involved in this research, perform cutting-edge research, present results, and meet with industry representatives to discuss potential applications. Educational outreach activities include visits to reservations in rural areas to enhance Washington's workforce diversity in science and technology. Technical description: The project builds on the discovery of persistent photoconductivity in annealed strontium titanate single crystals. This phenomenon is unique because the enhanced conductivity is large, very persistent, and occurs at room temperature. It is tentatively attributed to the excitation of an electron from a defect level to the conduction band, with an extremely low recapture rate though, the exact origin and behavior of this defect is currently unrevealed. The primary goals of this research project are: (i) to elucidate the defect physics behind persistent photoconductivity, and (ii) to use the persistent photoconductivity to optically define reconfigurable circuits. A variety of experimental methods, including Hall effect, infrared spectroscopy, and photoluminescence, are used to study the persistent photoconductivity and the defects responsible for it. Lithographic and confocal-microscopy techniques are utilized to write circuits on the crystal surface and in the interior, respectively. This approach could provide a basis for 3D electronic architectures, with current paths and active devices throughout the bulk of an oxide crystal.